General pharmacology
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General pharmacology · Oct 2000
Quantification of pulmonary capillary endothelium-bound angiotensin converting enzyme inhibition in man.
Angiotensin converting enzyme (ACE, kininase II) is an endothelial luminal ectoenzyme expressed abundantly on the pulmonary capillary endothelium and recognized as the site for the conversion of circulating angiotensin I to II. In the present study, we have applied recently developed methodologies for assaying pulmonary capillary endothelium-bound (PCEB) ACE activity in man, to estimate the interaction of an ACE inhibitor (enalaprilat) with PCEB ACE in human subjects. Trace amounts of the specific ACE substrate, 3H-benzoyl-Phe-Ala-Pro (3H-BPAP; 40 Ci or 2 nmol), was injected as a bolus into the subclavian vein and immediately blood was withdrawn from a radial arterial catheter. ⋯ This treatment had no significant effect on mean arterial pressure (91+/- 6 vs. 84 +/- 7 vs. 88 +/- 6 mm Hg for T(0), T(15) and T(120), respectively), but significantly decreased serum and PCEB ACE activities. When normalized to predrug (T(0)) activity levels, enalaprilat inhibited PCEB and serum ACE activities at T(15) 74 +/- 6% and 68 +/- 6%, respectively. However, 2 h after enalaprilat (T(120)), PCEB ACE inhibition was maintained at 66 +/- 7%, whereas serum ACE inhibition was reduced to 46 +/- 8% (P<.01 from PCEB ACE), suggesting a preferential PCEB ACE inhibitory effect of enalaprilat.